JP4293431B2 - Vehicle control apparatus and vehicle control method - Google Patents

Description

【００２３】
この数式１は、車輪の力学特性を示すタイヤモデルに基づき、車輪に作用する横力Ｆyを車輪すべり角βwで二次近似した式である。同数式において、係数ｋは、実験的に求めることができる定数であり、車輪と路面との間の摩擦係数μおよび上下力Ｆzに依存して変化する（数式２）。
【数２】

【００２４】
この係数ｋは車輪の特性を示す値であり、この値が高いと車輪の剛性が高いことを意味し、また、値が小さいと車輪の剛性が低いことを意味する。同数式から分かるように、係数ｋは、車輪すべり角βwが０における横力Ｆyの傾き（微分値）である。以下、この値を基準コーナリングパワーｋと称する。
【００２５】
一方、横力Ｆyの取り得る最大値である横力最大値Ｆymaxは、上下力Ｆz、前後力Ｆxおよび摩擦係数μから、数式３に基づき算出される。
【数３】

【００２６】
また、コーナリングパワーｋaは、ある車輪すべり角βwにおける横力Ｆyの傾き（微分値）であるので、コーナリングパワーｋaは、数式１を車輪すべり角βwで微分した数式４として表すことができる。
【数４】

【００２７】
数式１〜４から分かるように、車輪に作用する前後力Ｆx、横力Ｆyおよび上下力Ｆzと、摩擦係数μとが既知となれば、車輪すべり角βwは、一意に特定される。この車輪すべり角βwが特定されると、車輪のコーナリングパワーｋaは、車輪すべり角βwと横力Ｆyとの関係に基づいて、一義的に算出することができる。
【００２８】
つぎに、前後力Ｆx（または上下力Ｆz）とコーナリングパワーｋaとの関係について説明する。前後力Ｆxとコーナリングパワーｋaとの関係は、数式１および数式４から車輪すべり角βwを消去することにより、数式５として表すことができる。
【数５】

【００２９】
ここで、同数式中のＦymaxを数式３で置換すると、数式５は数式６となる。
【数６】

【００３０】
このコーナリングパワーｋaの傾向を見るため、数式６の分数部分を摩擦係数μと上下力Ｆzとの積（μ・Ｆz）で割り、無次元化する（数式７）。
【数７】

【００３１】
図３は、前後力Ｆxとコーナリングパワーｋaとの関係を示した図である。同図は数式７をグラフ化したものであり、縦軸はコーナリングパワーｋaを表し、横軸は無次元化した前後力（Ｆx／μＦz）を表している。なお、説明の便宜上、コーナリングパワーｋaを基準コーナリングパワーｋで割ることにより、縦軸も無次元化されている。同図では、横軸上を０から１へ向かう程、前後力Ｆxが大きくなることを意味し、縦軸上を０から１へ向かう程、コーナリングパワーｋaが大きくなることを意味する。また、同図には、数式７における分子部分（Ｆy／μＦz）の値を0.2，0.4，0.6，0.8とした場合の、前後力Ｆxとコーナリングパワーｋaとの関係がそれぞれ実線で示されている。各実線はこの分子部分（Ｆy／μＦz）の値に拘わらず基本的に同じ傾向を示すものの、この値（Ｆy／μＦz）が大きくなるに従い、前後力Ｆxとコーナリングパワーｋaとの関係は相対的に小さくなっている。同図から分かるように、コーナリングパワーｋaは、前後力Ｆxが小さくなる程その値が大きくなり、前後力Ｆxが大きくなる程その値が小さくなる。したがって、車輪のコーナリングパワーｋaを大きくするためには、車輪に作用する前後力Ｆxを小さくすればよいことになる。前後力Ｆxの調整は、車輪に加えられる駆動力または制動力を制御することにより行うことができる。
【００３２】
４つの車輪を備えた一般的な車両において、車輪に駆動力（または制動力）が定常的に加えられている状態を想定する。各車輪に作用する前後力Ｆxの総和は一定であるため、ある車輪に作用する前後力Ｆxを小さくすると、これに応じて他の車輪に作用する前後力Ｆxが大きくなる。そのため、各車輪に作用する前後力Ｆxのすべてを小さくするは困難であり、それ故に、各車輪のコーナリングパワーｋaのすべてを大きくすることもまた困難である。そこで、本実施形態では、左右輪に対する前後力配分比ｒxを変化させることで、左右輪の各コーナリングパワーｋaの代表値（例えば、平均値）が、現在の値よりも大きくなるような（好ましくは、最大値となるような）制御を行うことにする（左右輪のコーナリングパワーｋaの最大化）。
【００３３】
図４は、正規化された左右輪のコーナリングパワーの平均値ｋa_aveと左右輪の前後力配分比ｒxとの関係を示す図である。同図には、一例として、左旋回時の内輪（左前輪）と外輪（右前輪）とに関するこれらの関係が示されている。以下、左前輪のコーナリングパワーｋaをコーナリングパワーｋa_fl、右前輪のコーナリングパワーｋaをコーナリングパワーｋa_frと記述し、各車輪のコーナリングパワーｋaを区別する。同図に示す関係は、数式７に基づき算出される各コーナリングパワーｋa_fl，ｋa_frから、左右輪のコーナリングパワーの平均値ｋa_ave（（ｋa_fl＋ｋa_fr）/2）と、前後力配分比ｒxとの関係を導き出すことにより、一義的に求めることができる。左右輪のコーナリングパワーの平均値ｋa_aveを縦軸、前後力配分比ｒxを横軸に設定した場合、両者の関係は、ある前後力配分比ｒx（ｒx0）において極大値（ｋa_avemax）を有する、上に凸のグラフとなる。なお、車両が左旋回をしている場合、極大値となり得る前後力配分比ｒx0は、前後力配分比ｒxが左右輪に対して一対一となる位置よりも外（右）輪偏重寄りに存在する。
【００３４】
同図を参照し、左右輪に対する前後力配分比ｒxによるコーナリングパワーの平均値ｋa_aveの変化率Δｋについて考える。この変化率Δｋは、ある前後力配分比ｒxにおけるコーナリングパワーの平均値ｋa_aveの接線（直線Ｌ1）に関する傾き（微分値）である。具体的には、この直線Ｌ1は、前後力配分比ｒxが最も内輪偏重（左輪偏重）の場合に最も右上がりの直線（Δｋ：正の値）となり、前後力配分比ｒxが外輪偏重（右輪偏重）になるに従い、その傾きが水平に近づいていく。前後力配分比ｒx0において、直線Ｌ1は、水平な直線（Δｋ：０）となり、前後力配分比ｒxがさらに外輪偏重（右輪偏重）になるに従い、右下がりの直線となっていく。そして、前後力配分比ｒxが最も外輪偏重（右輪偏重）の場合に、直線Ｌ1は、最も右下がりの直線（Δｋ：負の値）となる。
【００３５】
ここで、現在の前後力配分比ｒxを、例えば、左右輪に対して一対一の状態（前後力配分比ｒx1）と考える。図４に示すように、車両が左旋回をしている場合、この配分比ｒx1は前後力配分比ｒx0よりも内（左）輪偏重寄りに位置するため、直線Ｌ1は右上がりの傾向を示し、変化率Δｋは正の所定値となる。この前後力配分比ｒxにおいて、左右輪のコーナリングパワーの平均値ｋa_aveを大きくするためには、直線Ｌ1の傾きがなだらかになる方向に（Δｋが減少する方向に）、前後力配分比ｒxを変化させる必要がある。同図に示す例では、前後力配分比ｒxを現在の前後力配分比ｒx1よりも外輪偏重にすれば、直線Ｌ1の傾きがなだらかになり（Δｋが減少し）、コーナリングパワーの平均値ｋa_aveは極大値ｋa_avemaxに向かって大きくなる。したがって、どのような走行状況であっても、変化率Δｋを０に近づける方向に前後力配分比ｒxを変化させれば、コーナリングパワーの平均値ｋa_aveは、極大値ｋa_avemaxに向かって大きくなることになる（好ましくは、極大値ｋa_avemaxと一致する）。
【００３６】
上記の変化率Δｋは、以下に示す数式８として表すことができる。
【数８】

【００３７】
数式８において、ｋ_flは左前輪の基準コーナリングパワーｋであり、ｋ_frは右前輪の基準コーナリングパワーｋである。一方、ｋc_flは、左前輪に関する無次元化した前後力Ｆx／μＦzによる無次元化したコーナリングパワーｋa_fl／ｋ_flの変化率（以下、単に「左前輪変化率ｋc_fl」という）である。また、ｋc_frは、右前輪に関する無次元化した前後力Ｆx／μＦzによる無次元化したコーナリングパワーｋa_fr／ｋ_frの変化率（以下、単に「右前輪変化率ｋc_fr」という）である。数式８から分かるように、変化率Δｋは、右前輪変化率ｋc_frと右前輪の基準コーナリングパワーｋ_frとの積（ｋc_fr・ｋ_fr）と、左前輪変化率ｋc_flと左前輪の基準コーナリングパワーｋ_flとの積（ｋc_fl・ｋ_fl）との差に比例する。したがって、この変化率Δｋを０に近づけるためには、これらの積ｋc_fr・ｋ_fr，ｋc_fl・ｋ_flの値が近づけばよいことになる。
【００３８】
図５はコーナリングパワーｋaと前後力Ｆxとの関係を示した図であり、図３と同様、横軸（前後力Ｆx）および縦軸（コーナリングパワーｋa）は無次元化されている。図４と同様に、前後力配分比ｒxが左右輪に対して一対一の状況で車両が左旋回をしていると考える。同図には、内輪（左前輪）のコーナリングパワーｋa_flと前後力Ｆxとの関係が実線で示されており、外輪（右前輪）のコーナリングパワーｋa_frと前後力Ｆxとの関係が点線で示されている。同図において、上述の左前輪変化率ｋc_flは、ある前後力Ｆxにおける左前輪のコーナリングパワーｋa_flの接線（直線Ｌ2）に関する傾き（微分値）に相当する。また、右前輪変化率ｋc_frは、ある前後力Ｆxにおける右前輪のコーナリングパワーｋa_frの接線（直線Ｌ3）に関する傾き（微分値）に相当する。図５において、縦軸は無次元化されているが、正規化されたコーナリングパワーｋa_fl（またはｋa_fr）を縦軸とした場合、各直線Ｌ2，Ｌ3の傾きはそれぞれｋc_fl・ｋ_fl（直線Ｌ2）、ｋc_fr・ｋ_fr（直線Ｌ3）となる。したがって、上記数式８に示す変化率Δｋを０に近づけることは、直線Ｌ2の傾き（左前輪変化率ｋc_fl）と直線Ｌ3の傾き（右前輪変化率ｋc_fr）とを近づけることと等価である。
【００３９】
そこで、前後力Ｆxの変化に応じた各変化率ｋc_fl，ｋc_frの傾向について考えてみる。左右前輪のコーナリングパワーｋa_fl，ｋa_frと前後力Ｆxとの関係は、値の大小はあるものの基本的に同じグラフ傾向を示すため、前後力Ｆxの変化に応じた各変化率ｋc_fl，ｋc_frの傾向も同じと考えることができる。そのため、ここでは、前後力Ｆxの変化に応じた左前輪変化率ｋc_flの傾向についてのみ考える。左前輪に作用する前後力Ｆxが最大の場合、直線Ｌ2は傾きが急な右下がりの直線となり、左前輪変化率ｋc_flは最小値（負の値）をとなる。この状態から左前輪に作用する前後力Ｆxが小さくなっていくと、直線Ｌ2は傾きなだらかな直線へと変わっていき、左前輪変化率ｋc_flは大きくなる。そして、左前輪に作用する前後力Ｆxが０の場合、直線Ｌ2は傾きが最もなだらになり、左前輪変化率ｋc_flは最大値（負の値）となる。
【００４０】
例えば、図５に示すように、左前輪変化率ｋc_flが右前輪変化率ｋc_frよりも小さい場合（ｋc_fr＞ｋc_fl）、すなわち、直線Ｌ2が直線Ｌ3よりも傾きが急な場合について考える。これらの直線Ｌ2，Ｌ3の傾きを近づけるためには、左前輪の前後力Ｆxを小さくすることで、直線Ｌ2の傾きを現在の傾きよりもなだらかな方向へ変えるとともに、右前輪の前後力Ｆxを大きくすることで、直線Ｌ3の傾きを現在の傾きよりも急な方向へ変えればよい。換言すれば、左前輪変化率ｋc_flと、右前輪変化率ｋc_frとを比較して、変化率が小さい一方の車輪（図５に示す例では左前輪）に作用する前後力Ｆxを小さくし、変化率が大きい他方の車輪（図５に示す例では右前輪）に作用する前後力Ｆxを大きくすればよい。これにより、直線Ｌ2の傾き（左前輪変化率ｋc_fl）と直線Ｌ3の傾き（右前輪変化率ｋc_fr）とが近づく方向に作用し、上記Δｋが０に近づく方向に作用する。そのため、本実施形態では、このような知得に基づき、現在の前後力配分比ｒxから所定量分だけ配分比を変化させることにより、Δｋが０に近づくような目標前後力配分比ｒx’を決定する。そして、車輪に作用する前後力が目標前後力配分比ｒx’となるように、駆動力（制動力）配分比Ｒxを制御する。例えば、図５に示す例では、現在の前後力配分比ｒxよりも右輪偏重となるように、目標前後力配分比ｒx’を決定するといった如くである。
【００４１】
再び図３を参照すると、無次元化されたグラフからは、上下力Ｆzとコーナリングパワーkaとの関係も把握することができる。同図において、横軸上を０から１へ向かう程、上下力Ｆzが小さくなることを意味する。コーナリングパワーｋaは、上下力Ｆzが小さくなる程その値が小さくなり、上下力Ｆzが大きくなる程その値が大きくなる。すなわち、車輪のコーナリングパワーｋaを大きくするためには、車輪に作用する上下力Ｆzを大きくすればよいことになる。上下力Ｆzの調整は、車輪にかかる垂直荷重を制御することにより行うことができる。ただし、上述した前後力Ｆxと同様、各車輪に作用する上下力Ｆzの総和は一定である。そこで、左右輪に対する上下力配分比ｒzを調整することにより、コーナリングパワーｋaの最大化を図ることにする。
【００４２】
図３に示す関係は無次元化したものであるため、正規化された左右輪のコーナリングパワーの平均値ｋa_aveと左右輪に対する上下力配分比ｒzとの関係も、図４と同様の傾向を示す。すなわち、左右輪のコーナリングパワーの平均値ｋa_aveを縦軸、上下力配分比ｒzを横軸に設定した場合、両者の関係は、ある上下力配分比ｒz（ｒz0（ｒx0に相当））において極大値（ｋa_avemax）を有する、上に凸のグラフとなる。したがって、変化率Δｋを０に近づける方向に上下力配分比ｒzを変化させれば、コーナリングパワーの平均値ｋa_aveは、極大値ｋa_avemaxに向かって大きくなる。この変化率Δｋを０に近づけるためには、数式８に示した各積ｋc_fr・ｋ_fr，ｋc_fl・ｋ_flが値として近づけばよいことになる。
【００４３】
図５は、無次元化されているため、上下力Ｆzとコーナリングパワーｋaとの関係も理解することができる。例えば、同図に示すように、現在の左前輪変化率ｋc_flが右前輪変化率ｋc_frよりも小さい場合（ｋc_fr＞ｋc_fl）、すなわち、直線Ｌ2が直線Ｌ3よりも傾きが急な場合について考える。これらの直線Ｌ2，Ｌ3の傾きを近づけるためには、左前輪の上下力Ｆzを大きくすることで、直線Ｌ2の傾きを現在の傾きよりもなだらかな方向へ変えるとともに、右前輪の上下力Ｆzを小さくするで、直線Ｌ3の傾きを現在の傾きよりも急な方向へ変えればよい。換言すれば、左前輪変化率ｋc_flと、右前輪変化率ｋc_frとを比較して、変化率が小さい一方の車輪（図５に示す例では左車輪）に作用する上下力Ｆzを大きくし、変化率が大きい他方の車輪（図５に示す例では右車輪）に作用する上下力Ｆzを小さくすればよい。これにより、直線Ｌ2の傾き（左前輪変化率ｋc_fl）と直線Ｌ3の傾き（右前輪変化率ｋc_fr）とが近づく方向に作用し、上記Δｋが０に近づく方向に作用する。そこで、本実施形態では、現在の上下力配分比ｒzから所定量分だけ配分比を変化させることにより、Δｋが０に近づくような目標上下力配分比ｒz’を決定する。そして、車輪に作用する上下力が目標上下力配分比ｒz’となるように、垂直荷重配分比Ｒzを制御することとする。例えば、図５に示す例では、現在の上下力配分比ｒzよりも左輪偏重となるように、目標上下力配分比ｒz’を決定するといった如くである。
【００４４】
以上のような車両制御の概念を踏まえた上で、再び図１を参照して、本実施形態にかかる車両制御装置のシステム構成について説明する。車両制御装置としては、ＣＰＵ、ＲＡＭ、ＲＯＭ、入出力インターフェースなどで構成されたマイクロコンピュータを用いることができる。車両制御装置は、ＲＯＭに記憶された制御プログラムに従い、上述した制御値（例えば、前後力配分比ｒx、上下力配分比ｒz）に関する演算を行う。そして、この演算によって算出された制御値に応じた駆動力（制動力）配分比または垂直荷重配分比が演算され、この演算結果に応じた制御信号が各種アクチュエータに対して出力される。車両制御装置には、このような演算を行うために、検出部１から得られる車輪に作用する作用力、特定部２から得られる車輪と路面との間の摩擦係数μが入力されている。また、この車両制御装置には、センサ３，４から得られた車両状態信号（エンジン回転数Ｎe、アクセル開度θacc）およびセンサ５から得られた現在のトランスミッションのギヤ位置を示すギヤ位置信号Ｐがさらに入力されている。
【００４５】
検出部１は、車輪に接続する車軸に取付けられた少なくとも一つ以上の応力検出センサ（例えば、抵抗歪ゲージ）と、この応力検出センサからの検出信号を処理する信号処理回路とで構成される。この検出部１は各車輪に設けられており、各車輪に関する作用力が車両制御装置に対して入力される。作用力に起因して車軸に生じる応力はこの作用力に比例するという知得に基づき、検出部１は、応力を通じて作用力を検出する。検出部１によって検出される作用力は、横力Ｆy、前後力Ｆxおよび上下力Ｆzの３つである。なお、図１において、検出部１は便宜上一つのブロックとして明記されているが、このブロックは各車輪に設けられる検出部１のすべてを総括している。検出部１に関する詳細な構成については、特開平４−３３１３３６号公報に記載されているので、必要ならば参照されたい。
【００４６】
特定部２は、車輪と路面との間の摩擦係数μを特定する。本実施形態において、特定部２は、上述した検出部１からの出力情報を用いることにより、路面摩擦力（すなわち、前後力Ｆx）と上下力Ｆzとの比として摩擦係数μを特定する。ただし、摩擦係数μを特定する場合、特定部２は、検出部１からの出力値に基づいてこれを特定する以外に、周知の手法を用いて推定してもよい。摩擦係数μを推定する手法としては、例えば、現在の車両のヨーレート、舵角、横加速度および車速を、種々の摩擦係数μにおけるこれらの値と比較することにより、推定する手法が挙げられる。このような推定手法の一例は、本出願人によって既に提案されている特開平８−２２７４号公報に開示されているので、必要ならば参照されたい。なお、検出部１が自身の検出結果に基づいて摩擦係数μを算出するのであれば、図１に示す特定部２を省略し、検出部１が特定部２としての機能を果たしてもよい。
【００４７】
マイクロコンピュータを機能的に捉えた場合、この車両制御装置は、推定部６と、処理部７と、制御部８〜１０とで構成される。推定部６は、各車輪について検出された作用力Ｆx，Ｆy，Ｆzと、特定された摩擦係数μとを読み込む。そして、この読み込まれた値に基づいて、各車輪のコーナリングパワーｋaを算出する。処理部７は、各車輪のコーナリングパワーｋaに基づいて算出される、左右の車輪のコーナリングパワーの平均値ｋa_aveが、左右輪の車輪のコーナリングパワーの平均値ｋa_aveの現在値よりも大きくなるように、前後力配分比ｒx（または上下力配分比ｒz）を決定する。具体的には、処理部７は、左右の車輪毎に、前後力Ｆx（または上下力Ｆz）によるコーナリングパワーｋaの変化率ｋc_fl，ｋc_frを算出する。そして、算出された左右の車輪に関する変化率ｋc_fl，ｋc_frに基づき、左車輪に関する変化率ｋc_flと、右車輪に関する変化率ｋc_frとが近づくように、前後力配分比ｒx（または上下力配分比ｒz）が決定される。この決定された前後力配分比ｒx（または上下力配分比ｒz）は、制御信号として制御部８〜１０のいずれかに対して出力される。
【００４８】
この制御部８〜１０はトルク配分制御部８、ブレーキ制御部９およびサスペンション制御部１０で構成されており、各制御部８〜１０は制御対象となる車両の状態に応じて適宜使い分けられる。例えば、処理部７が演算を行うことにより、所定の前後力配分比ｒxを決定した場合、処理部７はこの値に応じた制御信号をトルク配分制御部８またはブレーキ制御部９に対して出力する。これにより、トルク配分制御部８がトルク配分機構１１を制御する、或いは、ブレーキ制御部９がブレーキ機構１２を制御することにより、左右輪に対する駆動力配分比（または制動力配分比）Ｒxが制御される。また、処理部７が演算を行うことにより、所定の上下力配分比ｒzを決定した場合、処理部７はこの値に応じた制御信号をサスペンション制御部１０に対して出力する。これにより、サスペンション制御部１０がサスペンション機構１３を制御することにより、左右輪に対する垂直荷重配分比Ｒzが制御される。
【００４９】
図６は、本実施形態にかかる車両制御の手順を示したフローチャートである。このフローチャートに示した処理は、所定間隔毎に呼び出され、マイクロコンピュータによって実行される。以下、同図を参照し、本実施形態にかかるシステム処理を説明するが、ここでは、前輪における左右輪の前後力配分比ｒxを制御することにより、前輪に関する左右輪のコーナリングパワーｋaを最大化する手法について説明する。まず、ステップ１において、推定部６は摩擦係数μを読み込む。そして、推定部６は、検出部１からのセンサ信号から、前後力Ｆx、横力Ｆyおよび上下力Ｆzを読み込む（ステップ２）。つぎに、読み込まれた情報を用い、上記の数式４に基づいて、各車輪のコーナリングパワーｋaが算出される（ステップ３）。
【００５０】
ステップ４において、算出された各車輪のコーナリングパワーｋaに基づいて、左前輪に関する前後力Ｆxによるコーナリングパワーｋa_flの変化率（左前輪変化率）ｋc_flが算出される。具体的には、左前輪変化率ｋc_flは、算出された左前輪のコーナリングパワーｋa_flに基づいて、この値ｋa_flに対応した接線（例えば、図５に示した直線Ｌ2）に関する傾き（微分値）として算出される。また、右前輪に関する前後力Ｆxによるコーナリングパワーｋa_frの変化率（右前輪変化率）ｋc_frが同様の手法により算出される。
【００５１】
ステップ５において、左前輪変化率ｋc_flと右前輪変化率ｋc_frとの差の絶対値が、所定の判定値ｋcthよりも大きいか否かが判定される。このような判定処理を設ける理由は、各変化率ｋc_fl，ｋc_frが現段階で近似している場合には、すでに左右輪のコーナリングパワーの平均値ｋa_aveが最大付近となっている可能性が高く、あえて車両の状態を変える必要がないからである。そのため、このような状況での制御を回避すべく、ステップ６、７の処理に先立ち、コーナリングパワーｋaを最大化する必要があるか否かの判定が行われる。
【００５２】
上記の判定値ｋcthは、左前輪変化率ｋc_flと右前輪変化率ｋc_frとが実質的に同一と見なせる程度の、各変化率ｋc_fl，ｋc_frの差の絶対値に関する最大値として、実験やシミュレーションを通じて予め設定されている。したがって、この判定により肯定された場合（すなわち、左前輪変化率ｋc_flと右前輪変化率ｋc_frとの差の絶対値が判定値ｋcthよりも大きい場合）には、このステップ５に続くステップ６に進む。一方、この判定により否定された場合（左前輪変化率ｋc_flと右前輪変化率ｋc_frとの差分の絶対値が判定値ｋcth以下である場合）、ステップ６、７をスキップして本ルーチンを抜ける。
【００５３】
ステップ５に続くステップ６において、現在の左右前輪における前後力配分比ｒxに基づいて、目標前後力配分比ｒx’が決定される。具体的には、まず、算出された左右前輪の各変化率ｋc_fl，ｋc_frが比較される。そして、現在の前後力配分比ｒxよりも、変化率が小さい一方の車輪に作用する前後力Ｆxを小さく、変化率が大きい他方の車輪に作用する前後力Ｆxを大きくするような値として、目標前後力配分比ｒx’が求められる。例えば、図５に示したように、左前輪変化率ｋc_flよりも右前輪変化率ｋc_frの方が大きい状況では、現在の前後力配分比ｒxよりもステップ値相当だけ右前輪偏重となるように、目標前後力配分比ｒx’が算出される。一方、左前輪変化率ｋc_flよりも右前輪変化率ｋc_frが小さい状況では、現在の前後力配分比ｒxよりもステップ値相当だけ左前輪偏重となるように、目標前後力配分比ｒx’が算出される。
【００５４】
ステップ７において、決定された目標前後力配分比ｒx’に基づいて、左右前輪に対する駆動力配分比Ｒxが算出される。具体的には、まず、エンジン回転数Ｎeおよびスロットル開度θaccに基づいて、エンジン出力が推定される。つぎに、ギヤ位置Ｐに相当するギヤ比と乗算することにより、入力トルクＴiが算出される。そして、目標前後力配分比ｒx’と、入力トルクＴiとに基づき、前後輪に対するトルク配分比を考慮した上で、目標前後力配分比ｒx’となるような左右前輪に対するトルク配分比α（すなわち、駆動力配分比Ｒx）が算出される。そして、トルク配分制御部８は、決定された左右輪に対するトルク配分比αに応じた制御信号をトルク配分機構１１に対して出力し、本ルーチンを抜ける。
【００５５】
トルク配分機構（例えば、フロントデファレンシャル装置）１１は、出力された制御信号に応じて作動し、左右前輪に加えられるトルク配分を制御する。これにより、左右前輪に作用する前後力Ｆxがステップ値相当だけ調整された目標前後力配分比ｒx’となるように、駆動力配分比Ｒxが制御される。なお、車輪にかかる駆動力配分制御に関する詳細については、特開平８−２２７４号公報に開示されているので、必要ならば参照されたい。
【００５６】
このように、本実施形態によれば、左前輪に関する前後力Ｆxによるコーナリングパワーの変化率（左前輪変化率）ｋc_flと、右前輪に関する前後力Ｆxによるコーナリングパワーの変化率（右前輪変化率）ｋc_frとが算出される。つぎに、算出された各変化率ｋc_fl，ｋc_frを比較することにより、変化率が小さい一方の車輪に作用する前後力Ｆxを小さく、変化率が大きい他方の車輪に作用する前後力Ｆxを大きくするように、目標前後力配分比ｒx’が決定される。そして、車輪に作用する前後力Ｆxがこの目標前後力配分比ｒx’となるように、駆動力配分比Ｒxが制御される。これにより、車両の状態が変化し、左前輪変化率ｋc_flと、右前輪変化率ｋc_frとが近づく方向に作用することになり、左右前輪のコーナリングパワーの平均値ｋa_aveは、車両の状態を制御する前のそれよりも大きくなる。上述の如く、個々の車輪のコーナリングパワーｋaを個別で大きくすることは困難であるが、このような制御を行うことにより、前輪（または後輪）の全体でコーナリングパワーｋaを平均的に大きくすることができる。よって、挙動変化の応答性を速くすることができるので、例えば、コーナリングといった走行状況における車両の操安性の向上を図ることができる。
【００５７】
上述の実施形態では、前輪の左右輪を制御対象としてコーナリングパワーの平均値ｋa_aveの最大化を説明したが、同様の概念に基づいて、後輪の左右輪の左右輪を制御対象としてコーナリングパワーｋaの最大化を図ることもできる。また、前後輪のそれぞれの左右輪を制御対象として、コーナリングパワーｋaの最大化を図ってもよい。
【００５８】
また、制御の安定性を優先させる上で、ステップ値（微小値）相当の制御を行ったが、左前輪変化率ｋc_flと、右前輪変化率ｋc_frとが同じとなるような、目標前後力配分比ｒx’を直接的に求めてもよい。この目標前後力配分比ｒx’は、左前輪変化率ｋc_flと右前輪変化率ｋc_frとを等価と見なし、所定の数値演算を行うことにより一義的に求めることができる。ただし、かかる手法は、演算が複雑であり、処理の煩雑化につながるので、左前輪変化率ｋc_flと右前輪変化率ｋc_frとが同じとなるような目標前後力配分比ｒx’を、収束演算などに基づいて求めてもよい。
【００５９】
なお、本明細書では、左右輪のコーナリングパワーｋaの代表値として平均値を用いて説明したが、平均値以外にも、左右輪のコーナリングパワーｋaの総和または積などを用いてもよい。左右輪のコーナリングパワーｋaの総和または積を用いても基本的な概念は同じであり、左右輪のコーナリングパワーｋaの代表値が現在値よりも大きくなるように車両の状態を制御することにより、操安性の向上を図ることができる。
【００６０】
また、目標前後力配分比ｒx’となるように、車両の状態を制御をするのであれば、制動力配分比Ｒxを制御することにより、これを行うこともできる。かかる制御は、ブレーキ制御部９によって行われる。このブレーキ制御部９には、上述したトルク配分制御部８からの情報（すなわち、トルク配分比α）が入力されている。そのため、ブレーキ制御部９は、このトルク配分比αと、目標前後力配分比ｒx’とに基づいて、車輪に作用する前後力Ｆxが目標前後力配分比ｒx’となるように、制動力配分比Ｒxを算出する。そして、決定された制動力配分比Ｒxに応じた制御信号をブレーキ機構１２に対して出力する。これにより、ブレーキ機構（例えば、ＡＢＳ装置）１２が、ブレーキ制御部９から出力された制御信号に応じて作動し、車輪に加えられる制動力配分が制御される。具体的には、車輪に作用する前後力Ｆxがステップ値相当だけ調整された目標前後力配分比ｒx’となるように、制動力配分比Ｒxが制御される。これにより、左前輪変化率ｋc_flと、右前輪変化率ｋc_frとが近づく方向に作用することで、左右輪のコーナリングパワーの平均値ｋa_aveを現在のそれよりも大きくすることができる。
【００６１】
また、上述した説明では、左右輪に対する前後力配分比ｒxを調整することにより、左右輪のコーナリングパワーの最大化を説明した。しかしながら、上述した概念に基づき、左右輪に対する上下力配分比ｒzを調整することにより、左右輪のコーナリングパワーの最大化を図ってもよい。なお、システム処理の内容は、基本的に、図６に示す処理と同じであり、ここでの説明は省略する。特に相違する点は、処理部７が、ステップ値相当だけ変位させた目標上下力配分比ｒz’を決定することである。具体的には、左右の車輪に関する各変化率ｋc_fl，ｋc_frのうち、変化率が小さい一方の車輪に作用する上下力Ｆzを大きく、変化率が大きい他方の車輪に作用する上下力Ｆzを小さくするように、目標上下力配分比ｒz’が決定される。そして、決定された目標上下力配分比ｒz’に応じた制御信号が、サスペンション制御部１０に対して出力される。サスペンション制御部１０は、車輪に作用する上下力Ｆzが目標上下力配分比ｒz’となるように、左右輪に対する垂直荷重配分比Ｒzを決定し、決定した値に応じた制御信号をサスペンション機構１３に対して出力する。これにより、サスペンション機構１３が、サスペンション制御部１０から出力された制御信号に応じて作動し、車輪に加えられる垂直荷重配分zが制御される。具体的には、車輪に作用する上下力Ｆzがステップ値相当だけ調整された目標上下力配分比ｒz’となるように、垂直荷重配分比Ｒzが制御される。これにより、左前輪変化率ｋc_flと、右前輪変化率ｋc_frとが近づく方向に作用することで、左右輪のコーナリングパワーの平均値ｋa_aveを現在のそれよりも大きくすることができる。なお、車輪に作用する垂直荷重制御手法の詳細については、特開昭６２−２７５８１４号公報に開示されているので、必要ならば参照されたい。
【００６２】
本実施形態では、車輪すべり角βwと横力Ｆyとの関係をタイヤモデルを用い、これを二次近似することで定義したが、本発明はこれに限定されるものではない。例えば、車輪すべり角βwと横力Ｆyとの関係は、様々な条件下（前後力Ｆx、上下力Ｆzおよび摩擦係数μ）で実験的に求められるタイヤ特性を用いたり、別の数値モデル（Fialaモデル等）を用いたりして定義することもできる。図７は、実験的に算出された車輪すべり角βwと横力Ｆyとの関係の一例を示す説明図である。このような実験値を用いたとしても、車輪すべり角βwと横力Ｆyとの関係に基づき、車輪のコーナリングパワーｋaは、車輪すべり角βwの増加とともに増す横力Ｆyの割合（すなわち、微分値）として、一義的に算出される。
【００６３】
また、上述した実施形態では、コーナリングパワーｋaを、数式４として定義したが、数式９として簡略的に算出することができる。
【数９】

【００６４】
ここで、上述したコーナリングパワーｋaと区別するため、同数式に示すｋpを偽コーナリングパワーと称する。この偽コーナリングパワーｋpは、基本的に、数式４に示すコーナリングパワーｋaとほぼ同様な傾向を示す。したがって、上述した実施形態で用いたコーナリングパワーｋaに変えて、この偽コーナリングパワーｋpを用いても、同様の作用と効果とを奏することができる。
【００６５】
また、上述した検出部１は、車輪に作用する作用力を直接検出しているため、非線形性の要素が強いコーナリングパワーｋaを精度よく特定することができる。その結果、例えば、限界コーナリングといった走行状況であったとしても、或いは、低摩擦係数路面といった走行状況であったとしても、コーナリングパワーｋaを精度よく特定することができる。これにより、より有効に、コーナリングパワーの最大化を図ることができる。
【００６６】
（第２の実施形態）
第２の実施形態では、上述した左右輪のコーナリングパワーｋaの最大化を行うとともに、車両のスタビリティファクタを目標スタビリティファクタに近づけるように、制御値をさらに決定する。ここで、スタビリティファクタとは、車両のステア特性を示す評価値であり、コーナリング時の車両の挙動（すなわち、安定性）の目安となる値である。この値が正の場合、車両はアンダーステア傾向となり、この値が負の場合、車両はオーバーステア傾向となる。このスタビリティファクタの最適値は車両によって異なり、設計段階などにおいて設定される。このスタビリティファクタの最適値を常に追従するように車両が走行することで、車両の運動状態は適切に維持される。以下、左右輪のコーナリングパワーｋaの最大化と、スタビリティファクタとの関係について説明する。
【００６７】
図８は、車両に作用するモーメントを示す説明図である。操舵角一定で走行している車両を考えた場合、前輪に働く力Ｆfによって生じる車体周りのモーメントＭ1（Ｆf×ｌf，ｌf：車両の重心から前輪までの距離）と、後輪に働く力Ｆrによって生じる車体周りのモーメントＭ2（Ｆr×ｌr，ｌr：車両の重心から後輪までの距離）は、通常釣り合っている。この関係から、ステア特性を数式によって求める場合に使われる係数がスタビリティファクタである。しかしながら、第１の実施形態に示すように、前輪（或いは後輪）における左右輪の前後力配分比ｒxを変えると、車両には、この前後力配分比制御に応じたヨーモーメントが発生する。これにより、初期的には釣り合っていたモーメントＭ1，Ｍ2の釣り合いがくずれ、スタビリティファクタが最適値から外れてしまう虞がある。そこで、第２の実施形態では、左右輪に対する前後力配分比制御を加味した上で、現在の車両のスタビリティファクタが目標スタビリティファクタに近づくように車両の状態をさらに制御することにある。ここで、スタビリティファクタの基本形を数式１０に示す。
【数１０】

【００６８】
ここで、ｍは車両の質量、ｌfは前輪の車軸軸と車両の重心との間の距離、ｌrは後輪の車軸と車両の重心との間の距離である。また、ｋa_faveは、左前輪のコーナリングパワーをｋa_fl、右前輪のコーナリングパワーをｋa_frとした場合の、両コーナリングパワーｋa_fl，ｋa_frの平均値である。同様に、ｋa_raveは、左後輪のコーナリングパワーをｋa_rl、右後輪のコーナリングパワーをｋa_rrとした場合の、両コーナリングパワーｋa_rl，ｋa_rrの平均値である。
【００６９】
センサなどから求められるスタビリティファクタを実スタビリティファクタＡ1とすれば、左右輪の前後力配分比制御によるヨーモーメントを考慮した実スタビリティファクタＡ1は、下式で表すことができる。
【数１１】

【００７０】
ここで、ΔＦxは左右輪の前後力差（外輪の駆動力が大きい方向を正とする）であり、ｄはトレッド、ｙ”は横加速度である。また、検出部１または特定部２などにより求められる値には、記号の後ろに「1」が添えられている。
【００７１】
また、スタビリティファクタＡの最適値を目標スタビリティファクタＡ2とすると、実スタビリティファクタＡ1が目標スタビリティファクタＡ2に近づくようにするには、以下に示す数式１２が「０」に近づけばよい。
【数１２】

【００７２】
ここで、目標スタビリティファクタＡ2に関する各値ｋa_fave，ｋa_raveには、記号の後ろに「2」が添えられている。これらの値ｋa_fave2，ｋa_rave2は、目標スタビリティファクタＡ2に応じて予め設定されている値である。数式１２に示すΔＡが０に近づくためには、数式１３に示す等式が成り立つように、前輪のコーナリングパワーの平均値ｋa_fave1と、後輪のコーナリングパワーの平均値ｋa_rave1とを制御すればよい。
【数１３】

【００７３】
左右輪の前後力配分比ｒxを制御する以前に車両が目標スタビリティファクタＡ2を満たしていたと考えた場合、この前後力配分比制御により、仮想的に車両の重心位置が所定値（ΔＦx・ｄ／ｍ・ｙ”）だけ後方に移動したと考えることができる。数式１３を成立させるためには、前輪のコーナリングパワーの平均値ｋa_fave1を大きくし、後輪のコーナリングパワーの平均値ｋa_rave1を小さくすればよい。このようなコーナリングパワーを実現するためには、現在の前後輪に対する前後力配分比よりもステップ値相当だけ後輪偏重となるように、前後輪の前後力配分比を決定すればよいことになる。そして、前後輪に作用する前後力が、この決定された前後力配分比となるように、前後輪に対する駆動力配分比（或いは制動力配分比）を制御すればよい。あるいは、現在の上下力配分比よりもステップ値相当だけ前輪偏重となるように、前後輪の上下力配分比を決定してもよい。このケースでは、前後輪に作用する上下力が、この決定された前後力配分比となるように、前後輪に対する垂直荷重配分比を制御すればよい。
【００７４】
このように、ステップ値相当だけ、前後輪に対する前後力配分比または上下力配分比を制御することより、実スタビリティファクタＡ1が目標スタビリティに近づく方向に作用する。これにより、左右輪に対する前後力配分比制御に起因したヨーモーメントを相殺することができるので、左右輪に対する上下力配分比制御を行った場合でも、車両のステア特性が維持され、操安性の向上を図ることができる。なお、上述のヨーモーメントの発生は、基本的に、左右輪に関する駆動力配分比制御を行ったときに生じ得るので、左右輪に関する上下力配分比制御を行った場合には、このようなことは考慮する必要はない。
【００７５】
例えば、四輪駆動の車輪であれば、左右輪の前後力配分比制御に加え、前後輪の前後力配分比制御（または上下力配分比制御）を行うことにより、コーナリングパワーｋaの最大化を図りつつ、所定のスタビリティファクタを得ることができる。また、前輪（または後輪）駆動の車両であれば、左右輪の前後力配分制御に加え、前後輪の上下力配分比制御を行うことにより、コーナリングパワーｋaの最大化を図りつつ、所定のスタビリティファクタを得ることができる。
【００７６】
【発明の効果】
このように本発明では、左右の車輪のコーナリングパワーに着目し、これらのコーナリングパワーの代表値が、現在の値よりも大きくなるように車両の状態が制御される。個々の車輪のコーナリングパワーを個別で大きくすることは困難であるが、このような制御を行うことにより、左右の車輪全体でコーナリングパワーを大きくすることができる。これにより、挙動変化の応答性を速くすることができるので、例えば、コーナリングといった走行状況における車両の操安性の向上を図ることができる。
【図面の簡単な説明】
【図１】 本実施形態にかかる車両制御装置の全体構成を示したブロック構成図
【図２】 車輪に作用する作用力を示した説明図
【図３】 前後力とコーナリングパワーとの関係を示した図
【図４】 正規化された左右輪のコーナリングパワーの平均値と左右輪の前後力配分比との関係を示す図
【図５】 前後力とコーナリングパワーとの関係を示した図
【図６】 本実施形態にかかる車両制御の手順を示したフローチャート
【図７】 車輪すべり角と横力との関係の一例を示す説明図
【図８】 車両に作用するモーメントを示す説明図
【符号の説明】
１ 検出部
２ 特定部
３ センサ
４ センサ
５ センサ
６ 推定部
７ 処理部
８ トルク配分制御部
９ ブレーキ制御部
１０ サスペンション制御部
１１ トルク配分機構
１２ ブレーキ機構
１３ サスペンション機構[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle control device and a vehicle control method for controlling a motion state of a vehicle, and more particularly to control of a vehicle state based on cornering power of wheels.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there has been known a vehicle control method for controlling a motion state of a vehicle by controlling driving / braking torque applied to the wheel or controlling suspension characteristics of the wheel. In this vehicle control method, for example, in a driving situation such as cornering, control is performed so that the motion state of the vehicle is optimized, thereby improving the operability. One such technique is a vehicle control device that controls the motion state of a vehicle using a wheel frictional force utilization rate (see, for example, Patent Document 1). This vehicle control apparatus calculates | requires the wheel frictional force utilization factor of each wheel, and controls the wheel state of each wheel so that this wheel frictional force utilization factor approaches the target wheel frictional force utilization factor. This wheel friction force utilization rate is the maximum friction force (actual friction between the wheel and the road surface) of the actual friction force (the resultant force between the longitudinal force and the lateral force actually generated between the wheel and the road surface). (The product of the coefficient and the vertical force actually generated between the wheel and the road surface).
[0003]
[Patent Document 1]
Japanese Patent No. 3132190
[0004]
[Problems to be solved by the invention]
By the way, in order to effectively control the motion state of the vehicle in a traveling situation where the vehicle control is more effective (for example, cornering traveling or low friction coefficient road traveling), the present inventor We thought it was preferable to pay attention to cornering power. This is because the cornering power indicates the response of the vehicle behavior change (cornering force) depending on the magnitude of the value, and is closely related to the motion state of the vehicle. Therefore, the operability of the vehicle can be evaluated based on the cornering power. For example, cornering power is generally used in stability control and vehicle motion control using a vehicle motion model that takes into account only two degrees of freedom (a model that takes into account lateral translational motion and rotational motion around the vertical axis). It seems that formulation (for example, static margin, stability factor, etc.) is performed.
[0005]
The technique disclosed in Patent Document 1 improves the motion state of the vehicle by bringing the wheel frictional force utilization rate closer to the target frictional force utilization rate. However, even if the wheel friction force utilization factor of the wheel is brought close to the target friction utilization factor, if attention is paid to the cornering power of the wheel, the cornering power of the wheel at this time becomes an inappropriate value for each wheel. there is a possibility. For example, when the cornering power of the wheel is reduced, the controllability of the vehicle may be impaired.
[0006]
The present invention has been made in view of such circumstances, and an object thereof is to provide a novel vehicle control method.
[0007]
Another object of the present invention is to improve vehicle operability in a running state such as cornering by controlling the state of the vehicle based on the cornering power of the left and right wheels.
[0008]
[Means for Solving the Problems]
In order to solve such a problem, a first invention is a vehicle control device that controls a motion state of a vehicle, and includes a detection unit, a specifying unit, an estimation unit, a processing unit, and a control unit. I will provide a. In this vehicle control device, the detection unit detects an acting force including a longitudinal force, a lateral force, and a vertical force acting on the wheels. The specifying unit specifies a friction coefficient between the wheel and the road surface. The estimation unit estimates the cornering powers of the left and right wheels based on the detected acting force and the identified friction coefficient. The processing unit is calculated based on the estimated cornering power, so that the representative value of the cornering power for the left and right wheels is larger than the current value of the representative value of the cornering power for the left and right wheels. Represents the force distribution ratio for the left and right wheels A first control value is determined. The control unit controls the state of the vehicle based on the determined first control value.
[0009]
Moreover, 2nd invention provides the vehicle control apparatus which has a detection part, the specific | specification part, an estimation part, a process part, and a control part in the vehicle control apparatus which controls the motion state of a vehicle. In this vehicle control device, the detection unit detects an acting force including a longitudinal force, a lateral force, and a vertical force acting on the wheels. The specifying unit specifies a friction coefficient between the wheel and the road surface. The estimation unit estimates the cornering powers of the left and right wheels based on the detected acting force and the identified friction coefficient. The processing unit calculates the change rate of the cornering power due to the acting force for each of the left and right wheels based on the estimated cornering power, and based on the calculated change rate for the left and right wheels, The first control value is determined so that the rate of change related to the right wheel approaches. The control unit controls the state of the vehicle based on the determined first control value.
[0010]
Here, in the second invention, the processing unit calculates the change rate of the cornering power due to the longitudinal force as the change rate, and compares the calculated change rates related to the left and right wheels as the first control value. The longitudinal force distribution ratio for the left and right wheels is preferably determined so that the longitudinal force acting on one of the left and right wheels is small and the longitudinal force acting on the other wheel is large. Further, it is desirable that the control unit controls the driving force distribution ratio or the braking force distribution ratio for the left and right wheels so that the longitudinal force acting on the wheels becomes the determined longitudinal force distribution ratio. In this case, the rate of change for one wheel is preferably smaller than the rate of change for the other wheel.
[0011]
Further, in the second invention, the processing unit calculates the change rate of the cornering power due to the vertical force as the change rate, and compares the calculated change rates related to the left and right wheels as the first control value, It is preferable to determine the vertical force distribution ratio for the left and right wheels so that the vertical force acting on one of the left and right wheels is small and the vertical force acting on the other wheel is large. It is desirable that the controller controls the vertical load distribution ratio for the left and right wheels so that the vertical force acting on the wheels becomes the determined vertical force distribution ratio. In this case, the rate of change for one wheel is preferably greater than the rate of change for the other wheel.
[0012]
In the first or second invention, the processing unit further determines a second control value so that the vehicle stability factor approaches the target stability factor, and the control unit determines the determined second value. The state of the vehicle may be further controlled based on the control value. In this case, the processing unit determines the front / rear force distribution ratio with respect to the front and rear wheels as the second control value, and the control unit performs the front / rear force distribution ratio so that the front / rear force acting on the wheels becomes the determined front / rear force distribution ratio. It is preferable to further control the driving force distribution ratio or the braking force distribution ratio with respect to the wheels. Alternatively, the processing unit determines the vertical force distribution ratio for the front and rear wheels as the second control value, and the control unit determines that the vertical force acting on the wheels becomes the determined vertical force distribution ratio. It is desirable to further control the vertical load distribution ratio for the wheels.
[0013]
According to a third aspect of the present invention, there is provided a vehicle control method for controlling a motion state of a vehicle based on an acting force including a longitudinal force, a lateral force, and a vertical force acting on a wheel, and a friction coefficient between the wheel and a road surface. The first step of estimating the cornering power of each of the left and right wheels, and the representative value of the cornering power for the left and right wheels calculated based on the estimated cornering power is the representative of the cornering power for the left and right wheels. To be greater than the current value of the value, Represents the force distribution ratio for the left and right wheels A vehicle control method comprising: a second step of determining a first control value; and a third step of controlling the state of the vehicle based on the determined first control value. .
[0014]
According to a fourth aspect of the present invention, there is provided a vehicle control method for controlling a motion state of a vehicle, based on an acting force including a longitudinal force, a lateral force and a vertical force acting on a wheel, and a friction coefficient between the wheel and a road surface. Then, based on the first step of estimating the cornering power of the left and right wheels and the estimated cornering power, the change rate of the cornering power due to the acting force is calculated for each of the left and right wheels. The second step of determining the first control value based on the change rate related to the left wheel and the change rate related to the right wheel approach the change rate related to the left wheel and the determined first control value. And a third step of controlling the state of the vehicle on the basis of the vehicle control method.
[0015]
Here, in the fourth invention, the second step calculates the change rate of the cornering power due to the longitudinal force as the rate of change, and compares the calculated rate of change relating to the left and right wheels, thereby performing the first control. As a value, it is a step for determining the longitudinal force distribution ratio for the left and right wheels so that the longitudinal force acting on one of the left and right wheels is reduced and the longitudinal force acting on the other wheel is increased. Is preferred. The third step is preferably a step of controlling the driving force distribution ratio or the braking force distribution ratio with respect to the left and right wheels so that the longitudinal force acting on the wheels becomes the determined longitudinal force distribution ratio. In this case, the rate of change for one wheel is preferably smaller than the rate of change for the other wheel.
[0016]
In the fourth invention, the second step calculates the change rate of the cornering power due to the vertical force as the rate of change, and compares the calculated rate of change for the left and right wheels to thereby calculate the first control value. The vertical force distribution ratio for the left and right wheels is determined so that the vertical force acting on one of the left and right wheels is reduced and the vertical force acting on the other wheel is increased. preferable. The third step is preferably a step of controlling the vertical load distribution ratio for the left and right wheels so that the vertical force acting on the wheels becomes the determined vertical force distribution ratio. In this case, the rate of change for one wheel is preferably greater than the rate of change for the other wheel.
[0017]
In the third or fourth aspect of the invention, the second step further includes a fourth step of determining a second control value such that the vehicle stability factor approaches the target stability factor, The step 3 may further include a fifth step of controlling the state of the vehicle based on the determined second control value. In this case, the fourth step is a step of determining the longitudinal force distribution ratio for the front and rear wheels as the second control value, and the fifth step is a longitudinal force distribution in which the longitudinal force acting on the wheels is determined. Preferably, the step is a step of further controlling the driving force distribution ratio or the braking force distribution ratio with respect to the front and rear wheels so that the ratio becomes the ratio. Alternatively, the fourth step is a step of determining the vertical force distribution ratio for the front and rear wheels as the second control value, and the fifth step is a vertical force distribution ratio in which the vertical force acting on the wheels is determined. It is desirable to further control the vertical load distribution ratio with respect to the front and rear wheels.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 is a block configuration diagram showing the overall configuration of the vehicle control apparatus according to the present embodiment. This vehicle control device determines the longitudinal force distribution ratio for the left and right wheels or the vertical force distribution ratio for the left and right wheels in consideration of the cornering power ka of the left and right wheels. The driving force distribution ratio (or braking force distribution ratio) for the left and right wheels is controlled so that the longitudinal force acting on the wheels becomes the determined longitudinal force distribution ratio. Alternatively, the vertical load distribution ratio with respect to the left and right wheels is controlled so that the vertical force acting on the wheels becomes the determined vertical force distribution ratio. Thereby, since the state of the vehicle (that is, the state amount of the wheel) changes, the cornering power ka of the left and right wheels acts in a direction approaching a desired value, and the operability of the vehicle can be improved. . First, in order to clarify the concept of vehicle control according to the present embodiment, the cornering power ka will be described, and then a specific system configuration and system processing of the vehicle control device will be described.
[0019]
The cornering power ka is a lateral force Fy due to a slight change in the wheel slip angle βw (a component force generated in a direction perpendicular to the wheel center plane among the frictional force generated on the ground contact surface when the wheel turns at a certain slip angle βw). ) Change rate. That is, the cornering power ka can be defined as the slope (differential value) of the lateral force Fy at a certain wheel slip angle βw. Therefore, the cornering power ka can be uniquely derived based on the relationship between the wheel slip angle βw and the lateral force Fy. The cornering power ka is a parameter that has a great influence on the maneuverability of the vehicle. When this value is large, the response of the change in the behavior of the vehicle to the steering becomes fast, and when this value is small, the response of the change in the behavior of the vehicle to the steering. Sex is slow. For example, when cornering traveling or traveling on a road surface with a low friction coefficient, it is desirable that the response of the behavior change be fast, and basically it is preferable that the cornering power ka is large.
[0020]
FIG. 2 is an explanatory diagram showing the acting force acting on the wheel. As shown in the figure, the acting force related to the wheel includes a longitudinal force Fx, a cornering force and the like in addition to the lateral force Fy described above. When the wheel turns at a certain slip angle βw, the component force generated in the direction parallel to the wheel center plane among the frictional force generated on the ground contact surface is the longitudinal force Fx, which is generated in the direction perpendicular to the wheel traveling direction. The component force is the cornering force. Further, although not clearly shown in the drawing, the acting force relating to the wheel may further include a load in the vertical direction, so-called vertical force Fz (not shown).
[0021]
Of these forces listed as acting forces, the lateral force Fy and the cornering force can be treated as relatively similar forces. The lateral force Fy and the cornering force do not have a one-to-one correspondence as values, but practically both values are approximated within the range of the wheel slip angle βw that the vehicle can take. In this specification, the cornering force and the lateral force Fy are regarded as substantially the same, and the lateral force Fy is used as a base. corner Consider ring power ka. That is, if the relationship between the lateral force Fy and the cornering power ka is known in advance, the cornering power ka is uniquely specified based on the lateral force Fy. Hereafter, the lateral force Fy corner Consider the relationship with the ring power ka.
[0022]
The wheel slip angle βw and the lateral force Fy acting on the wheel satisfy Expression 1 shown below.
[Expression 1]

[0023]
Formula 1 is a formula obtained by quadratic approximation of the lateral force Fy acting on the wheel with a wheel slip angle βw based on a tire model indicating the dynamic characteristics of the wheel. In the equation, the coefficient k is a constant that can be obtained experimentally, and varies depending on the friction coefficient μ between the wheel and the road surface and the vertical force Fz (Equation 2).
[Expression 2]

[0024]
The coefficient k is a value indicating the characteristics of the wheel. A high value means that the wheel has high rigidity, and a small value means that the wheel has low rigidity. As can be seen from the equation, the coefficient k is the slope (differential value) of the lateral force Fy when the wheel slip angle βw is zero. Hereinafter, this value is referred to as a reference cornering power k.
[0025]
On the other hand, the lateral force maximum value Fymax, which is the maximum value that the lateral force Fy can take, is calculated based on Formula 3 from the vertical force Fz, the longitudinal force Fx, and the friction coefficient μ.
[Equation 3]

[0026]
Further, since the cornering power ka is the slope (differential value) of the lateral force Fy at a certain wheel slip angle βw, the cornering power ka can be expressed as Formula 4 obtained by differentiating Formula 1 with the wheel slip angle βw.
[Expression 4]

[0027]
As can be seen from Equations 1 to 4, if the longitudinal force Fx, lateral force Fy, vertical force Fz acting on the wheel, and friction coefficient μ are known, the wheel slip angle βw is uniquely identified. When the wheel slip angle βw is specified, the cornering power ka of the wheel can be uniquely calculated based on the relationship between the wheel slip angle βw and the lateral force Fy.
[0028]
Next, the relationship between the longitudinal force Fx (or vertical force Fz) and the cornering power ka will be described. The relationship between the longitudinal force Fx and the cornering power ka can be expressed as Equation 5 by eliminating the wheel slip angle βw from Equation 1 and Equation 4.
[Equation 5]

[0029]
Here, when Fymax in the equation is replaced with Equation 3, Equation 5 becomes Equation 6.
[Formula 6]

[0030]
In order to see the tendency of the cornering power ka, the fractional part of Equation 6 is divided by the product of the friction coefficient μ and the vertical force Fz (μ · Fz) to make it dimensionless (Equation 7).
[Expression 7]

[0031]
FIG. 3 is a diagram showing the relationship between the longitudinal force Fx and the cornering power ka. This figure is a graph of Equation 7. The vertical axis represents the cornering power ka, and the horizontal axis represents the dimensionless longitudinal force (Fx / μFz). For convenience of explanation, the vertical axis is also made dimensionless by dividing the cornering power ka by the reference cornering power k. In the figure, it means that the longitudinal force Fx increases as it goes from 0 to 1 on the horizontal axis, and the cornering power ka increases as it goes from 0 to 1 on the vertical axis. In the same figure, the solid line represents the relationship between the longitudinal force Fx and the cornering power ka when the value of the molecular part (Fy / μFz) in Equation 7 is 0.2, 0.4, 0.6, 0.8. . Each solid line shows basically the same tendency regardless of the value of this molecular part (Fy / μFz), but as this value (Fy / μFz) increases, the relationship between the longitudinal force Fx and the cornering power ka is relative. It is getting smaller. As can be seen from the figure, the cornering power ka increases as the longitudinal force Fx decreases, and decreases as the longitudinal force Fx increases. Therefore, in order to increase the cornering power ka of the wheel, the longitudinal force Fx acting on the wheel may be reduced. The longitudinal force Fx can be adjusted by controlling the driving force or braking force applied to the wheels.
[0032]
In a general vehicle having four wheels, it is assumed that a driving force (or braking force) is constantly applied to the wheels. Since the total sum of the longitudinal force Fx acting on each wheel is constant, if the longitudinal force Fx acting on a certain wheel is reduced, the longitudinal force Fx acting on the other wheel is increased accordingly. For this reason, it is difficult to reduce all of the longitudinal force Fx acting on each wheel, and therefore it is also difficult to increase all of the cornering power ka of each wheel. Therefore, in the present embodiment, by changing the longitudinal force distribution ratio rx for the left and right wheels, the representative value (for example, the average value) of each cornering power ka of the left and right wheels is larger than the current value (preferably Will be controlled (maximizing the cornering power ka of the left and right wheels).
[0033]
FIG. 4 is a diagram showing the relationship between the normalized average power ka_ave of the left and right wheels and the longitudinal force distribution ratio rx of the left and right wheels. In the figure, as an example, the relationship between the inner wheel (left front wheel) and the outer wheel (right front wheel) when turning left is shown. Hereinafter, the cornering power ka of the left front wheel is described as cornering power ka_fl and the cornering power ka of the right front wheel is described as cornering power ka_fr, and the cornering power ka of each wheel is distinguished. The relationship shown in the figure is derived from the respective cornering powers ka_fl and ka_fr calculated based on Expression 7, and the relationship between the average value ka_ave ((ka_fl + ka_fr) / 2) of the left and right wheels and the longitudinal force distribution ratio rx. This can be determined uniquely. When the average value ka_ave of the left and right wheel cornering power is set on the vertical axis and the longitudinal force distribution ratio rx is set on the horizontal axis, the relationship between them has a maximum value (ka_avemax) at a certain longitudinal force distribution ratio rx (rx0). The graph becomes convex. When the vehicle is turning left, the front / rear force distribution ratio rx0 that can be the maximum value exists closer to the outer (right) wheel than the position where the front / rear force distribution ratio rx is one-to-one with respect to the left and right wheels. To do.
[0034]
With reference to this figure, the change rate Δk of the average value ka_ave of the cornering power according to the longitudinal force distribution ratio rx for the left and right wheels will be considered. This rate of change Δk is an inclination (differential value) with respect to a tangent (straight line L1) of the average value ka_ave of the cornering power at a certain longitudinal force distribution ratio rx. Specifically, this straight line L1 is the straight line (Δk: positive value) that rises to the most right when the front / rear force distribution ratio rx is the innermost wheel load (left wheel load), and the front / rear force distribution ratio rx is the outer wheel load (right). The inclination becomes closer to the horizontal as the wheel becomes more uneven. In the front / rear force distribution ratio rx0, the straight line L1 becomes a horizontal straight line (Δk: 0), and becomes a straight line descending to the right as the front / rear force distribution ratio rx becomes more eccentric to the outer wheel (right wheel). When the longitudinal force distribution ratio rx is the outermost wheel load (right wheel load), the straight line L1 is the rightmost straight line (Δk: negative value).
[0035]
Here, the current longitudinal force distribution ratio rx is considered to be, for example, a one-to-one state (front / rear force distribution ratio rx1) with respect to the left and right wheels. As shown in FIG. 4, when the vehicle is turning left, the distribution ratio rx1 is located closer to the inner (left) wheel than the front / rear force distribution ratio rx0, so the straight line L1 shows a tendency to rise to the right. The change rate Δk is a positive predetermined value. In order to increase the average value ka_ave of the cornering power of the left and right wheels at this longitudinal force distribution ratio rx, the longitudinal force distribution ratio rx is changed in the direction in which the slope of the straight line L1 becomes gentle (in the direction in which Δk decreases). It is necessary to let In the example shown in the figure, if the front / rear force distribution ratio rx is set to be more eccentric than the current front / rear force distribution ratio rx1, the slope of the straight line L1 becomes gentle (Δk decreases), and the average value ka_ave of the cornering power is It increases toward the maximum value ka_avemax. Therefore, in any driving situation, if the longitudinal force distribution ratio rx is changed in a direction that brings the rate of change Δk closer to 0, the average value ka_ave of the cornering power increases toward the maximum value ka_avemax. (Preferably coincident with the maximum value ka_avemax).
[0036]
The rate of change Δk can be expressed as Equation 8 shown below.
[Equation 8]

[0037]
In Equation 8, k_fl is the reference cornering power k of the left front wheel, and k_fr is the reference cornering power k of the right front wheel. On the other hand, kc_fl is the rate of change of the dimensionless cornering power ka_fl / k_fl due to the dimensionless longitudinal force Fx / μFz related to the left front wheel (hereinafter simply referred to as “left front wheel rate of change kc_fl”). Kc_fr is a rate of change of the dimensionless cornering power ka_fr / k_fr by the dimensionless longitudinal force Fx / μFz related to the right front wheel (hereinafter simply referred to as “right front wheel rate of change kc_fr”). As can be seen from Equation 8, the change rate Δk is the product of the right front wheel change rate kc_fr and the right front wheel reference cornering power k_fr (kc_fr · k_fr), the left front wheel change rate kc_fl and the left front wheel reference cornering power k_fl. It is proportional to the difference from the product (kc_fl · k_fl). Therefore, in order to bring this rate of change Δk close to 0, the values of these products kc_fr · k_fr, kc_fl · k_fl need only be close.
[0038]
FIG. 5 is a diagram showing the relationship between the cornering power ka and the longitudinal force Fx. As in FIG. 3, the horizontal axis (longitudinal force Fx) and the vertical axis (cornering power ka) are dimensionless. As in FIG. 4, it is assumed that the vehicle is turning left in a situation where the front / rear force distribution ratio rx is one-to-one with respect to the left and right wheels. In the figure, the relationship between the cornering power ka_fl of the inner ring (left front wheel) and the longitudinal force Fx is indicated by a solid line, and the relationship between the cornering power ka_fr of the outer ring (right front wheel) and the longitudinal force Fx is indicated by a dotted line. ing. In the figure, the left front wheel change rate kc_fl described above corresponds to a slope (differential value) with respect to the tangent (straight line L2) of the cornering power ka_fl of the left front wheel at a certain longitudinal force Fx. Further, the right front wheel change rate kc_fr corresponds to a slope (differential value) with respect to a tangent line (straight line L3) of the cornering power ka_fr of the right front wheel at a certain longitudinal force Fx. In FIG. 5, the vertical axis is dimensionless, but when the normalized cornering power ka_fl (or ka_fr) is the vertical axis, the slopes of the straight lines L2 and L3 are kc_fl · k_fl (straight line L2), respectively. kc_fr · k_fr (straight line L3). Therefore, bringing the rate of change Δk shown in Equation 8 closer to 0 is equivalent to bringing the slope of the straight line L2 (left front wheel change rate kc_fl) close to the slope of the straight line L3 (right front wheel change rate kc_fr).
[0039]
Thus, let us consider the tendency of each change rate kc_fl, kc_fr according to the change in the longitudinal force Fx. The relationship between the cornering powers ka_fl, ka_fr of the left and right front wheels and the longitudinal force Fx shows basically the same graph trend although the values are large, so the tendency of each change rate kc_fl, kc_fr according to the variation of the longitudinal force Fx is also It can be considered the same. Therefore, here, only the tendency of the left front wheel change rate kc_fl according to the change of the longitudinal force Fx will be considered. When the longitudinal force Fx acting on the left front wheel is maximum, the straight line L2 is a straight line with a steep downward slope to the right, and the left front wheel change rate kc_fl has a minimum value (negative value). As the longitudinal force Fx acting on the left front wheel decreases from this state, the straight line L2 changes to a straight line with a gentle slope, and the left front wheel change rate kc_fl increases. When the longitudinal force Fx acting on the left front wheel is zero, the straight line L2 has the most gentle inclination, and the left front wheel change rate kc_fl has the maximum value (negative value).
[0040]
For example, as shown in FIG. 5, consider the case where the left front wheel change rate kc_fl is smaller than the right front wheel change rate kc_fr (kc_fr> kc_fl), that is, the straight line L2 is steeper than the straight line L3. In order to make the inclinations of these straight lines L2 and L3 closer, by reducing the front / rear force Fx of the left front wheel, the inclination of the straight line L2 is changed to a gentler direction than the current inclination, and the front / rear force Fx of the right front wheel is changed. By increasing the value, the inclination of the straight line L3 may be changed in a direction steeper than the current inclination. In other words, the left front wheel change rate kc_fl and the right front wheel change rate kc_fr are compared, and the longitudinal force Fx acting on one of the wheels having the smaller change rate (the left front wheel in the example shown in FIG. 5) is reduced. The longitudinal force Fx acting on the other wheel (the right front wheel in the example shown in FIG. 5) having a large rate may be increased. As a result, the slope of the straight line L2 (left front wheel change rate kc_fl) and the slope of the straight line L3 (right front wheel change rate kc_fr) act in a direction approaching, and Δk acts in a direction approaching zero. Therefore, in this embodiment, based on such knowledge, the target longitudinal force distribution ratio rx ′ such that Δk approaches 0 is obtained by changing the distribution ratio by a predetermined amount from the current longitudinal force distribution ratio rx. decide. Then, the driving force (braking force) distribution ratio Rx is controlled so that the longitudinal force acting on the wheels becomes the target longitudinal force distribution ratio rx ′. For example, in the example shown in FIG. 5, the target longitudinal force distribution ratio rx ′ is determined such that the right wheel is more deviated than the current longitudinal force distribution ratio rx.
[0041]
Referring to FIG. 3 again, the relationship between the vertical force Fz and the cornering power ka can also be grasped from the dimensionless graph. In the same figure, it means that the vertical force Fz becomes smaller as it goes from 0 to 1 on the horizontal axis. The cornering power ka decreases as the vertical force Fz decreases, and increases as the vertical force Fz increases. That is, in order to increase the cornering power ka of the wheel, the vertical force Fz acting on the wheel may be increased. The vertical force Fz can be adjusted by controlling the vertical load applied to the wheel. However, as with the longitudinal force Fx described above, the sum of the vertical forces Fz acting on each wheel is constant. Therefore, the cornering power ka is maximized by adjusting the vertical force distribution ratio rz for the left and right wheels.
[0042]
Since the relationship shown in FIG. 3 is non-dimensional, the relationship between the normalized average power ka_ave of the left and right wheels and the vertical force distribution ratio rz for the left and right wheels also shows the same tendency as in FIG. . That is, when the average value ka_ave of the left and right wheels is set to the vertical axis and the vertical force distribution ratio rz is set to the horizontal axis, the relationship between them is a maximum value at a certain vertical force distribution ratio rz (rz0 (corresponding to rx0)). This is an upwardly convex graph with (ka_avemax). Therefore, if the vertical force distribution ratio rz is changed in the direction in which the change rate Δk is close to 0, the average value ka_ave of the cornering power increases toward the maximum value ka_avemax. In order to bring this rate of change Δk closer to 0, the products kc_fr · k_fr, kc_fl · k_fl shown in Equation 8 need only be closer to each other as values.
[0043]
Since FIG. 5 is dimensionless, it is possible to understand the relationship between the vertical force Fz and the cornering power ka. For example, as shown in the figure, consider the case where the current left front wheel change rate kc_fl is smaller than the right front wheel change rate kc_fr (kc_fr> kc_fl), that is, the straight line L2 is steeper than the straight line L3. In order to make the inclinations of these straight lines L2 and L3 closer, by increasing the vertical force Fz of the left front wheel, the inclination of the straight line L2 is changed to a gentler direction than the current inclination, and the vertical force Fz of the right front wheel is changed. It is sufficient to change the inclination of the straight line L3 in a direction steeper than the current inclination. In other words, the left front wheel change rate kc_fl and the right front wheel change rate kc_fr are compared, and the vertical force Fz acting on one wheel having a small change rate (the left wheel in the example shown in FIG. 5) is increased and changed. The vertical force Fz acting on the other wheel having the larger rate (the right wheel in the example shown in FIG. 5) may be reduced. As a result, the slope of the straight line L2 (left front wheel change rate kc_fl) and the slope of the straight line L3 (right front wheel change rate kc_fr) act in a direction approaching, and Δk acts in a direction approaching zero. Therefore, in this embodiment, by changing the distribution ratio by a predetermined amount from the current vertical force distribution ratio rz, the target vertical force distribution ratio rz ′ is determined so that Δk approaches zero. Then, the vertical load distribution ratio Rz is controlled so that the vertical force acting on the wheels becomes the target vertical force distribution ratio rz ′. For example, in the example shown in FIG. 5, the target vertical force distribution ratio rz ′ is determined so that the left wheel is more deviated than the current vertical force distribution ratio rz.
[0044]
Based on the concept of vehicle control as described above, the system configuration of the vehicle control apparatus according to the present embodiment will be described with reference to FIG. 1 again. As the vehicle control device, a microcomputer composed of a CPU, a RAM, a ROM, an input / output interface, and the like can be used. The vehicle control device performs calculations related to the above-described control values (for example, the longitudinal force distribution ratio rx and the vertical force distribution ratio rz) according to a control program stored in the ROM. Then, a driving force (braking force) distribution ratio or a vertical load distribution ratio corresponding to the control value calculated by this calculation is calculated, and control signals corresponding to the calculation result are output to various actuators. In order to perform such calculation, the vehicle control device is input with the acting force acting on the wheel obtained from the detection unit 1 and the friction coefficient μ between the wheel obtained from the specifying unit 2 and the road surface. In addition, the vehicle control device includes a vehicle state signal (engine speed Ne, accelerator opening θacc) obtained from the sensors 3 and 4 and a gear position signal P indicating the current gear position of the transmission obtained from the sensor 5. Is further entered.
[0045]
The detection unit 1 includes at least one stress detection sensor (for example, a resistance strain gauge) attached to an axle connected to a wheel, and a signal processing circuit that processes a detection signal from the stress detection sensor. . This detection part 1 is provided in each wheel, and the action force regarding each wheel is input with respect to a vehicle control apparatus. Based on the knowledge that the stress generated in the axle due to the acting force is proportional to the acting force, the detection unit 1 detects the acting force through the stress. The acting force detected by the detection unit 1 is three, that is, a lateral force Fy, a longitudinal force Fx, and a vertical force Fz. In FIG. 1, the detection unit 1 is clearly shown as one block for convenience, but this block summarizes all the detection units 1 provided on each wheel. The detailed configuration of the detection unit 1 is described in Japanese Patent Application Laid-Open No. 4-331336, so please refer to it if necessary.
[0046]
The specifying unit 2 specifies the friction coefficient μ between the wheel and the road surface. In the present embodiment, the specifying unit 2 specifies the friction coefficient μ as a ratio between the road surface friction force (that is, the longitudinal force Fx) and the vertical force Fz by using the output information from the detection unit 1 described above. However, when specifying the friction coefficient μ, the specifying unit 2 may estimate the friction coefficient μ using a well-known method in addition to specifying this based on the output value from the detecting unit 1. As a method for estimating the friction coefficient μ, for example, there is a method for estimating the current vehicle yaw rate, steering angle, lateral acceleration, and vehicle speed by comparing these values with various friction coefficients μ. An example of such an estimation method is disclosed in Japanese Patent Laid-Open No. 8-2274 which has already been proposed by the applicant of the present application. If the detection unit 1 calculates the friction coefficient μ based on its detection result, the specification unit 2 shown in FIG. 1 may be omitted, and the detection unit 1 may function as the specification unit 2.
[0047]
When the microcomputer is functionally grasped, the vehicle control device includes an estimation unit 6, a processing unit 7, and control units 8 to 10. The estimation unit 6 reads the acting forces Fx, Fy, Fz detected for each wheel and the identified friction coefficient μ. Then, the cornering power ka of each wheel is calculated based on the read value. The processing unit 7 calculates the mean value ka_ave of the cornering power of the left and right wheels, which is calculated based on the cornering power ka of each wheel, to be larger than the current value of the mean value ka_ave of the cornering power of the left and right wheels. The longitudinal force distribution ratio rx (or the vertical force distribution ratio rz) is determined. Specifically, the processing unit 7 calculates the change rates kc_fl and kc_fr of the cornering power ka due to the longitudinal force Fx (or the vertical force Fz) for each of the left and right wheels. Then, based on the calculated change rates kc_fl and kc_fr related to the left and right wheels, the longitudinal force distribution ratio rx (or the vertical force distribution ratio rz) so that the change rate kc_fl related to the left wheel approaches the change rate kc_fr related to the right wheel. Is determined. The determined longitudinal force distribution ratio rx (or vertical force distribution ratio rz) is output as a control signal to one of the control units 8 to 10.
[0048]
The control units 8 to 10 include a torque distribution control unit 8, a brake control unit 9, and a suspension control unit 10, and the control units 8 to 10 are appropriately used according to the state of the vehicle to be controlled. For example, when the processing unit 7 performs a calculation to determine a predetermined longitudinal force distribution ratio rx, the processing unit 7 outputs a control signal corresponding to this value to the torque distribution control unit 8 or the brake control unit 9. To do. As a result, the torque distribution control unit 8 controls the torque distribution mechanism 11 or the brake control unit 9 controls the brake mechanism 12 to control the driving force distribution ratio (or braking force distribution ratio) Rx for the left and right wheels. Is done. In addition, when the processing unit 7 performs a calculation to determine a predetermined vertical force distribution ratio rz, the processing unit 7 outputs a control signal corresponding to this value to the suspension control unit 10. As a result, the suspension control unit 10 controls the suspension mechanism 13 to control the vertical load distribution ratio Rz for the left and right wheels.
[0049]
FIG. 6 is a flowchart showing a procedure of vehicle control according to the present embodiment. The processing shown in this flowchart is called at predetermined intervals and executed by the microcomputer. Hereinafter, the system processing according to the present embodiment will be described with reference to the same figure, but here, the cornering power ka of the left and right wheels for the front wheels is maximized by controlling the front / rear force distribution ratio rx of the left and right wheels. The method to do is demonstrated. First, in step 1, the estimation unit 6 reads the friction coefficient μ. And the estimation part 6 reads the longitudinal force Fx, the lateral force Fy, and the up-down force Fz from the sensor signal from the detection part 1 (step 2). Next, using the read information, the cornering power ka of each wheel is calculated based on Equation 4 above (step 3).
[0050]
In step 4, based on the calculated cornering power ka of each wheel, a change rate (left front wheel change rate) kc_fl of the cornering power ka_fl due to the longitudinal force Fx related to the left front wheel is calculated. Specifically, the left front wheel change rate kc_fl is based on the calculated cornering power ka_fl of the left front wheel as a slope (differential value) with respect to a tangent (for example, the straight line L2 shown in FIG. 5) corresponding to this value ka_fl. Calculated. Further, a change rate (right front wheel change rate) kc_fr of the cornering power ka_fr due to the longitudinal force Fx on the right front wheel is calculated by the same method.
[0051]
In step 5, it is determined whether or not the absolute value of the difference between the left front wheel change rate kc_fl and the right front wheel change rate kc_fr is greater than a predetermined determination value kcth. The reason why such a determination process is provided is that, when the respective change rates kc_fl and kc_fr are approximated at the present stage, there is a high possibility that the average value ka_ave of the cornering power of the left and right wheels is already near the maximum, This is because there is no need to change the state of the vehicle. Therefore, in order to avoid the control in such a situation, it is determined whether or not the cornering power ka needs to be maximized prior to the processing in steps 6 and 7.
[0052]
The determination value kcth is a maximum value regarding the absolute value of the difference between the change rates kc_fl and kc_fr so that the left front wheel change rate kc_fl and the right front wheel change rate kc_fr can be regarded as substantially the same. Is set. Therefore, when the determination is affirmative (that is, when the absolute value of the difference between the left front wheel change rate kc_fl and the right front wheel change rate kc_fr is larger than the determination value kcth), the process proceeds to step 6 following step 5. . On the other hand, when this determination is negative (when the absolute value of the difference between the left front wheel change rate kc_fl and the right front wheel change rate kc_fr is equal to or less than the determination value kcth), the routine skips steps 6 and 7 and exits from this routine.
[0053]
In step 6 following step 5, the target is calculated based on the front / rear force distribution ratio rx for the left and right front wheels. Before and after The force distribution ratio rx ′ is determined. Specifically, first, the calculated change rates kc_fl and kc_fr of the left and right front wheels are compared. The target longitudinal force Fx acting on one wheel having a small change rate is smaller than the current longitudinal force distribution ratio rx, and the longitudinal force Fx acting on the other wheel having a large change rate is increased. The longitudinal force distribution ratio rx ′ is obtained. For example, as shown in FIG. 5, in the situation where the right front wheel change rate kc_fr is larger than the left front wheel change rate kc_fl, the right front wheel is deviated by the step value rather than the current front / rear force distribution ratio rx. A target longitudinal force distribution ratio rx ′ is calculated. On the other hand, in a situation where the right front wheel change rate kc_fr is smaller than the left front wheel change rate kc_fl, the target front / rear force distribution ratio rx ′ is calculated so that the left front wheel is deviated by the step value from the current front / rear force distribution ratio rx. The
[0054]
In step 7, the driving force distribution ratio Rx for the left and right front wheels is calculated based on the determined target longitudinal force distribution ratio rx ′. Specifically, first, the engine output is estimated based on the engine speed Ne and the throttle opening θacc. Next, the input torque Ti is calculated by multiplying the gear ratio corresponding to the gear position P. Then, based on the target longitudinal force distribution ratio rx ′ and the input torque Ti, the torque distribution ratio α for the left and right front wheels (that is, the target longitudinal force distribution ratio rx ′ is considered after considering the torque distribution ratio for the front and rear wheels. , Driving force distribution ratio Rx) is calculated. Then, the torque distribution control unit 8 outputs a control signal corresponding to the determined torque distribution ratio α for the left and right wheels to the torque distribution mechanism 11 and exits from this routine.
[0055]
The torque distribution mechanism (for example, front differential device) 11 operates according to the output control signal, and controls the torque distribution applied to the left and right front wheels. Thus, the driving force distribution ratio Rx is controlled so that the longitudinal force Fx acting on the left and right front wheels becomes the target longitudinal force distribution ratio rx ′ adjusted by a step value. Details regarding the driving force distribution control applied to the wheels are disclosed in Japanese Patent Laid-Open No. 8-2274, so refer to them if necessary.
[0056]
Thus, according to the present embodiment, the rate of change in cornering power due to the longitudinal force Fx for the left front wheel (left front wheel rate of change) kc_fl and the rate of change in cornering power due to the longitudinal force Fx for the right front wheel (rate of change in the right front wheel). kc_fr is calculated. Next, by comparing the calculated change rates kc_fl and kc_fr, the longitudinal force Fx acting on one wheel having a small change rate is reduced, and the longitudinal force Fx acting on the other wheel having a large change rate is increased. As described above, the target longitudinal force distribution ratio rx ′ is determined. Then, the driving force distribution ratio Rx is controlled so that the longitudinal force Fx acting on the wheels becomes the target longitudinal force distribution ratio rx ′. As a result, the vehicle state changes, and the left front wheel change rate kc_fl and the right front wheel change rate kc_fr act in the approaching direction, and the average value ka_ave of the cornering power of the left and right front wheels controls the vehicle state. It becomes bigger than the previous one. As described above, it is difficult to individually increase the cornering power ka of each wheel. However, by performing such control, the cornering power ka of the entire front wheel (or rear wheel) is increased on average. be able to. Therefore, since the response of the behavior change can be increased, for example, it is possible to improve the operability of the vehicle in a driving situation such as cornering.
[0057]
In the above-described embodiment, the maximization of the average value ka_ave of the cornering power has been described with the left and right wheels of the front wheel being controlled. However, based on the same concept, the cornering power ka with the left and right wheels of the rear wheel being controlled is controlled. Can be maximized. Further, the cornering power ka may be maximized with the left and right wheels of the front and rear wheels being controlled.
[0058]
In addition, in order to prioritize the stability of the control, the control corresponding to the step value (small value) was performed, but the target longitudinal force distribution so that the left front wheel change rate kc_fl and the right front wheel change rate kc_fr are the same. The ratio rx ′ may be obtained directly. This target longitudinal force distribution ratio rx ′ can be uniquely obtained by assuming that the left front wheel change rate kc_fl and the right front wheel change rate kc_fr are equivalent, and performing a predetermined numerical calculation. However, since this method is complicated in calculation and leads to complicated processing, the target front / rear force distribution ratio rx ′ in which the left front wheel change rate kc_fl and the right front wheel change rate kc_fr are the same is calculated as the convergence calculation. You may ask based on.
[0059]
In the present specification, the average value is used as the representative value of the cornering power ka of the left and right wheels. However, in addition to the average value, the sum or product of the cornering power ka of the left and right wheels may be used. Even if the sum or product of the cornering power ka of the left and right wheels is used, the basic concept is the same. By controlling the vehicle state so that the representative value of the cornering power ka of the left and right wheels is larger than the current value, It is possible to improve the maneuverability.
[0060]
In addition, if the vehicle state is controlled so that the target longitudinal force distribution ratio rx ′ is obtained, this can also be performed by controlling the braking force distribution ratio Rx. Such control is performed by the brake control unit 9. Information (that is, torque distribution ratio α) from the torque distribution control unit 8 described above is input to the brake control unit 9. Therefore, the brake control unit 9 distributes the braking force based on the torque distribution ratio α and the target longitudinal force distribution ratio rx ′ so that the longitudinal force Fx acting on the wheels becomes the target longitudinal force distribution ratio rx ′. The ratio Rx is calculated. Then, a control signal corresponding to the determined braking force distribution ratio Rx is output to the brake mechanism 12. As a result, the brake mechanism (for example, the ABS device) 12 operates according to the control signal output from the brake control unit 9, and the distribution of the braking force applied to the wheels is controlled. This The Specifically, the braking force distribution ratio Rx is controlled so that the longitudinal force Fx acting on the wheel becomes the target longitudinal force distribution ratio rx ′ adjusted by a step value. As a result, the left front wheel change rate kc_fl and the right front wheel change rate kc_fr act in the approaching direction, whereby the average value ka_ave of the cornering power of the left and right wheels can be made larger than the current value.
[0061]
In the above description, the cornering power of the left and right wheels has been maximized by adjusting the longitudinal force distribution ratio rx for the left and right wheels. However, the cornering power of the left and right wheels may be maximized by adjusting the vertical force distribution ratio rz for the left and right wheels based on the concept described above. Note that the contents of the system processing are basically the same as the processing shown in FIG. 6, and a description thereof is omitted here. The difference is that the processing unit 7 determines a target vertical force distribution ratio rz ′ that is displaced by a step value. Specifically, out of the change rates kc_fl and kc_fr relating to the left and right wheels, the vertical force Fz acting on one wheel having a small change rate is increased, and the vertical force Fz acting on the other wheel having a large change rate is decreased. As described above, the target vertical force distribution ratio rz ′ is determined. Then, a control signal corresponding to the determined target vertical force distribution ratio rz ′ is output to the suspension control unit 10. The suspension control unit 10 determines the vertical load distribution ratio Rz for the left and right wheels so that the vertical force Fz acting on the wheels becomes the target vertical force distribution ratio rz ′, and sends a control signal corresponding to the determined value to the suspension mechanism 13. Output for. As a result, the suspension mechanism 13 operates in response to the control signal output from the suspension control unit 10, and the vertical load distribution z applied to the wheels is controlled. Specifically, the vertical load distribution ratio Rz is controlled so that the vertical force Fz acting on the wheel becomes the target vertical force distribution ratio rz ′ adjusted by a step value. As a result, the left front wheel change rate kc_fl and the right front wheel change rate kc_fr act in the approaching direction, whereby the average value ka_ave of the cornering power of the left and right wheels can be made larger than the current value. The details of the vertical load control method acting on the wheels are disclosed in Japanese Patent Application Laid-Open No. 62-275814, so refer to them if necessary.
[0062]
In this embodiment, the relationship between the wheel slip angle βw and the lateral force Fy is defined by using a tire model and quadratic approximation thereof, but the present invention is not limited to this. For example, the relationship between the wheel slip angle βw and the lateral force Fy can be obtained by using tire characteristics experimentally obtained under various conditions (longitudinal force Fx, vertical force Fz and friction coefficient μ), or by using another numerical model (Fiala It can also be defined using a model). FIG. 7 is an explanatory diagram showing an example of the relationship between the experimentally calculated wheel slip angle βw and the lateral force Fy. Even if such experimental values are used, the cornering power ka of the wheel is based on the relationship between the wheel slip angle βw and the lateral force Fy, and the wheel cornering power ka increases as the wheel slip angle βw increases (ie, the differential value). ) And is uniquely calculated.
[0063]
In the above-described embodiment, the cornering power ka is defined as Equation 4, but can be simply calculated as Equation 9.
[Equation 9]

[0064]
Here, in order to distinguish from the above-described cornering power ka, kp shown in the equation is referred to as a false cornering power. This false cornering power kp basically shows the same tendency as the cornering power ka shown in Equation 4. Therefore, even if this false cornering power kp is used instead of the cornering power ka used in the above-described embodiment, the same operation and effect can be achieved.
[0065]
Moreover, since the detection part 1 mentioned above has detected the acting force which acts on a wheel directly, it can pinpoint the cornering power ka with a strong nonlinear element accurately. As a result, for example, the cornering power ka can be specified with high accuracy even if the vehicle is in a driving situation such as limit cornering or in a driving situation such as a low friction coefficient road surface. Thereby, the cornering power can be maximized more effectively.
[0066]
(Second Embodiment)
In the second embodiment, the control value is further determined so as to maximize the cornering power ka of the left and right wheels and to bring the vehicle stability factor closer to the target stability factor. Here, the stability factor is an evaluation value that indicates the steering characteristic of the vehicle, and is a value that serves as a measure of the behavior (that is, stability) of the vehicle during cornering. When this value is positive, the vehicle tends to understeer, and when this value is negative, the vehicle tends to oversteer. The optimum value of the stability factor differs depending on the vehicle and is set at the design stage. When the vehicle travels so as to always follow the optimum value of the stability factor, the motion state of the vehicle is appropriately maintained. Hereinafter, the relationship between the maximization of the cornering power ka of the left and right wheels and the stability factor will be described.
[0067]
FIG. 8 is an explanatory diagram showing moments acting on the vehicle. Considering a vehicle traveling at a constant steering angle, the moment M1 around the vehicle body caused by the force Ff acting on the front wheel (Ff × lf, if: distance from the center of gravity of the vehicle to the front wheel) and the force Fr acting on the rear wheel The moment M2 (Fr × lr, lr: distance from the center of gravity of the vehicle to the rear wheel) generated by the vehicle is normally balanced. From this relationship, the coefficient used when the steer characteristic is obtained by an equation is the stability factor. However, as shown in the first embodiment, when the front / rear force distribution ratio rx of the left and right wheels in the front wheel (or rear wheel) is changed, a yaw moment corresponding to the front / rear force distribution ratio control is generated in the vehicle. As a result, the balance of moments M1 and M2 that were initially balanced may be lost, and the stability factor may deviate from the optimum value. Therefore, in the second embodiment, the vehicle state is further controlled so that the current vehicle stability factor approaches the target stability factor in consideration of the longitudinal force distribution ratio control for the left and right wheels. Here, the basic form of the stability factor is shown in Formula 10.
[Expression 10]

[0068]
Here, m is the mass of the vehicle, lf is the distance between the front axle and the center of gravity of the vehicle, and lr is the distance between the rear axle and the center of gravity of the vehicle. Further, ka_fave is an average value of the cornering powers ka_fl and ka_fr when the cornering power of the left front wheel is ka_fl and the cornering power of the right front wheel is ka_fr. Similarly, ka_rave is an average value of both cornering powers ka_rl and ka_rr when the cornering power of the left rear wheel is ka_rl and the cornering power of the right rear wheel is ka_rr.
[0069]
Assuming that the stability factor required from the sensor or the like is the actual stability factor A1, the actual stability factor A1 in consideration of the yaw moment by the longitudinal force distribution ratio control of the left and right wheels can be expressed by the following equation.
[Expression 11]

[0070]
Here, ΔFx is a difference between the front and rear forces of the left and right wheels (a direction in which the driving force of the outer wheel is large is positive), d is a tread, and y ″ is a lateral acceleration. The required value is preceded by a “1”.
[0071]
Further, assuming that the optimum value of the stability factor A is the target stability factor A2, in order for the actual stability factor A1 to approach the target stability factor A2, the following equation 12 should be close to “0”. .
[Expression 12]

[0072]
Here, each value ka_fave and ka_rave relating to the target stability factor A2 is appended with “2” after the symbol. These values ka_fave2 and ka_rave2 are values set in advance according to the target stability factor A2. In order for ΔA shown in Equation 12 to approach 0, the average value ka_fave1 of the front wheel cornering power and the average value ka_rave1 of the cornering power of the rear wheel may be controlled so that the equation shown in Equation 13 holds.
[Formula 13]

[0073]
If it is considered that the vehicle has satisfied the target stability factor A2 before controlling the front / rear force distribution ratio rx of the left and right wheels, the center of gravity position of the vehicle is virtually set to a predetermined value (ΔFx · d by this front / rear force distribution ratio control. / M · y ″) can be considered to have moved backward. In order to satisfy Equation 13, the average value ka_fave1 of the front wheel cornering power is increased and the average value ka_rave1 of the rear wheel cornering power is decreased. In order to realize such cornering power, it is only necessary to determine the front / rear wheel front / rear force distribution ratio so that the rear wheel is more deviated by a step value than the current front / rear wheel distribution ratio. If the driving force distribution ratio (or braking force distribution ratio) for the front and rear wheels is controlled so that the front / rear force acting on the front and rear wheels becomes the determined front / rear force distribution ratio. Alternatively, the vertical force distribution ratio of the front and rear wheels may be determined so that the front wheel is more deviated by the step value than the current vertical force distribution ratio.In this case, the vertical force acting on the front and rear wheels is The vertical load distribution ratio with respect to the front and rear wheels may be controlled so that the determined front / rear force distribution ratio is obtained.
[0074]
Thus, by controlling the longitudinal force distribution ratio or the vertical force distribution ratio with respect to the front and rear wheels by an amount corresponding to the step value, the actual stability factor A1 acts in a direction approaching the target stability. As a result, the yaw moment caused by the front / rear force distribution ratio control for the left and right wheels can be canceled out, so that even when the vertical force distribution ratio control for the left and right wheels is performed, the vehicle steering characteristics are maintained, and the operability is improved. Improvements can be made. The generation of the above-mentioned yaw moment can basically occur when the driving force distribution ratio control for the left and right wheels is performed. Therefore, this is the case when the vertical force distribution ratio control for the left and right wheels is performed. Does not need to be considered.
[0075]
For example, in the case of a four-wheel drive wheel, the cornering power ka is maximized by performing front / rear wheel front / rear force distribution ratio control (or vertical force distribution ratio control) in addition to front / rear wheel front / rear force distribution ratio control. A predetermined stability factor can be obtained while planning. Further, in the case of a vehicle driven by front wheels (or rear wheels), in addition to front / rear wheel front / rear force distribution control, front / rear wheel vertical force distribution ratio control is performed to maximize cornering power ka and Stability factor can be obtained.
[0076]
【The invention's effect】
Thus, in the present invention, focusing on the cornering power of the left and right wheels, the state of the vehicle is controlled such that the representative value of these cornering powers is greater than the current value. Although it is difficult to individually increase the cornering power of each wheel, the cornering power can be increased for the entire left and right wheels by performing such control. Thereby, since the responsiveness of a behavior change can be made quick, for example, it is possible to improve the operability of the vehicle in a driving situation such as cornering.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the overall configuration of a vehicle control device according to an embodiment.
FIG. 2 is an explanatory diagram showing the acting force acting on the wheel
FIG. 3 is a diagram showing the relationship between longitudinal force and cornering power.
FIG. 4 is a diagram showing the relationship between the averaged cornering power of the left and right wheels and the front / rear force distribution ratio of the left and right wheels
FIG. 5 is a diagram showing the relationship between longitudinal force and cornering power.
FIG. 6 is a flowchart showing a vehicle control procedure according to the embodiment.
FIG. 7 is an explanatory diagram showing an example of the relationship between wheel slip angle and lateral force.
FIG. 8 is an explanatory diagram showing moments acting on the vehicle
[Explanation of symbols]
1 detector
2 specific part
3 Sensor
4 Sensor
5 Sensor
6 Estimator
7 processing section
8 Torque distribution control unit
9 Brake control section
10 Suspension controller
11 Torque distribution mechanism
12 Brake mechanism
13 Suspension mechanism

Claims (18)

In a vehicle control device that controls a motion state of a vehicle,
A detecting unit for detecting an acting force including a longitudinal force, a lateral force and a vertical force acting on the wheel;
A specific part for specifying a friction coefficient between the wheel and the road surface;
An estimation unit that estimates the cornering power of each of the left and right wheels based on the detected acting force and the identified friction coefficient;
The acting force on the left and right wheels is calculated based on the estimated cornering power so that the representative value of the cornering power for the left and right wheels is larger than the current value of the representative value of the cornering power for the left and right wheels. A processing unit for determining a first control value representing a distribution ratio ;
And a controller that controls a state of the vehicle based on the determined first control value. In a vehicle control device that controls a motion state of a vehicle,
A detecting unit for detecting an acting force including a longitudinal force, a lateral force and a vertical force acting on the wheel;
A specific part for specifying a friction coefficient between the wheel and the road surface;
An estimation unit that estimates the cornering power of each of the left and right wheels based on the detected acting force and the identified friction coefficient;
Based on the estimated cornering power, the change rate of the cornering power due to the acting force is calculated for each left and right wheel, and based on the calculated change rate for the left and right wheels, the change rate for the left wheel, A processing unit that determines the first control value so that the rate of change related to the right wheel approaches,
And a controller that controls a state of the vehicle based on the determined first control value. The processing unit calculates, as the change rate, a change rate of cornering power due to longitudinal force, and compares the calculated change rates related to the left and right wheels. The longitudinal force distribution ratio for the left and right wheels is determined so that the longitudinal force acting on one of the wheels is small and the longitudinal force acting on the other wheel is large,
3. The control unit according to claim 2, wherein the control unit controls the driving force distribution ratio or the braking force distribution ratio with respect to the left and right wheels so that the longitudinal force acting on the wheels becomes the determined longitudinal force distribution ratio. The vehicle control apparatus described.   The vehicle control device according to claim 3, wherein a change rate related to the one wheel is smaller than a change rate related to the other wheel. The processing unit calculates, as the change rate, a change rate of cornering power due to vertical force, and compares the calculated change rates related to the left and right wheels, whereby the first control value is calculated as the left and right wheels. The vertical force distribution ratio for the left and right wheels is determined so that the vertical force acting on one wheel is small and the vertical force acting on the other wheel is large,
3. The vehicle control according to claim 2, wherein the control unit controls a vertical load distribution ratio for the left and right wheels so that a vertical force acting on the wheels becomes the determined vertical force distribution ratio. 4. apparatus.   The vehicle control apparatus according to claim 5, wherein a change rate related to the one wheel is larger than a change rate related to the other wheel. The processing unit further determines a second control value so that the vehicle stability factor approaches the target stability factor,
The vehicle control device according to claim 1, wherein the control unit further controls a state of the vehicle based on the determined second control value. The processing unit determines a longitudinal force distribution ratio for the front and rear wheels as the second control value,
The control unit further controls a driving force distribution ratio or a braking force distribution ratio with respect to the front and rear wheels so that a front / rear force acting on the wheels becomes the determined front / rear force distribution ratio. The vehicle control device described in 1. The processing unit determines a vertical force distribution ratio for front and rear wheels as the second control value,
The vehicle according to claim 7, wherein the control unit further controls a vertical load distribution ratio with respect to the front and rear wheels so that a vertical force acting on the wheels becomes the determined vertical force distribution ratio. Control device. In a vehicle control method for controlling a motion state of a vehicle,
A first step of estimating the cornering power of each of the left and right wheels based on an acting force including a longitudinal force, a lateral force and a vertical force acting on the wheel, and a friction coefficient between the wheel and the road surface;
The acting force on the left and right wheels is calculated based on the estimated cornering power so that the representative value of the cornering power for the left and right wheels is larger than the current value of the representative value of the cornering power for the left and right wheels. A second step of determining a first control value representing the distribution ratio ;
And a third step of controlling the state of the vehicle based on the determined first control value. In a vehicle control method for controlling a motion state of a vehicle,
A first step of estimating the cornering power of each of the left and right wheels based on an acting force including a longitudinal force, a lateral force and a vertical force acting on the wheel, and a friction coefficient between the wheel and the road surface;
Based on the estimated cornering power, the change rate of the cornering power due to the acting force is calculated for each left and right wheel, and based on the calculated change rate for the left and right wheels, the change rate for the left wheel, A second step of determining a first control value such that the rate of change with respect to the right wheel approaches;
And a third step of controlling the state of the vehicle based on the determined first control value. The second step calculates, as the rate of change, a rate of change of cornering power due to longitudinal force, and compares the calculated rate of change for the left and right wheels, thereby obtaining the left and right as the first control value. Determining the longitudinal force distribution ratio for the left and right wheels so that the longitudinal force acting on one of the wheels is reduced and the longitudinal force acting on the other wheel is increased;
The third step is a step of controlling the driving force distribution ratio or the braking force distribution ratio with respect to the left and right wheels so that the longitudinal force acting on the wheels becomes the determined longitudinal force distribution ratio. The vehicle control method according to claim 11.   The vehicle control method according to claim 12, wherein a change rate related to the one wheel is smaller than a change rate related to the other wheel. The second step calculates, as the rate of change, a rate of change of cornering power due to vertical force, and compares the calculated rate of change for the left and right wheels as the first control value. Determining the vertical force distribution ratio for the left and right wheels so that the vertical force acting on one of the wheels is small and the vertical force acting on the other wheel is large,
The third step is a step of controlling the vertical load distribution ratio with respect to the left and right wheels so that the vertical force acting on the wheels becomes the determined vertical force distribution ratio. The vehicle control method described.   The vehicle control method according to claim 14, wherein a change rate related to the one wheel is larger than a change rate related to the other wheel. The second step further includes a fourth step of determining a second control value such that the vehicle stability factor approaches the target stability factor;
The vehicle control according to any one of claims 10 to 13, wherein the third step further includes a fifth step of controlling a state of the vehicle based on the determined second control value. Method. The fourth step is a step of determining a longitudinal force distribution ratio for the front and rear wheels as the second control value,
The fifth step is a step of controlling the driving force distribution ratio or the braking force distribution ratio with respect to the front and rear wheels so that the front / rear force acting on the wheels becomes the determined front / rear force distribution ratio. The vehicle control method according to claim 16. The fourth step is a step of determining a vertical force distribution ratio for the front and rear wheels as the second control value,
The fifth step is a step of controlling a vertical load distribution ratio for the front and rear wheels so that a vertical force acting on the wheels becomes the determined vertical force distribution ratio. The vehicle control method described.

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